125 a sub panel
#1
09-03-14, 04:57 PM
Join Date: Sep 2014
Location: usa
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125 a sub panel
Our oil fired tank less hot water system failed. I have purchased an eco smart tank less 27kv electric hot water heater. Our main circuit box has 200A service, but not enough space for the 3 40A breakers (2 pole) that the system requires. I want to install a 125A sub panel with the 3 40A breakers. What size wire do I need to run form the main box to the sub box that will be protected by a 125A breaker. It will be about a 25 foot run.
Thanks,
Kevin
Thanks,
Kevin
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#2
09-03-14, 05:12 PM
Welcome to the forums.
It's a shame the tankless heater is so far from the main panel. You would have been better off connecting the tankless heater right to the main panel and shed some of those circuits to the sub panel.
Your 125A sub panel is right at the edge of being too small. I consider that 27K load as a continuous load which means you need a supply of 135A.
I would use #1 wire as the supply wire. Are you going to run a conduit or do you need a cable size designation ?
It's a shame the tankless heater is so far from the main panel. You would have been better off connecting the tankless heater right to the main panel and shed some of those circuits to the sub panel.
Your 125A sub panel is right at the edge of being too small. I consider that 27K load as a continuous load which means you need a supply of 135A.
I would use #1 wire as the supply wire. Are you going to run a conduit or do you need a cable size designation ?
#3
09-03-14, 06:17 PM
Group Moderator
I highly doubt that a tank-less water heater will be running for 3 hours or more. I would not consider it a continuous load.
If you run conduit, you can use #2 copper. If you use an NM-b cable (copper) you need 1/0.
IF you want to use aluminum cable you need 2/0. If its XHHW AL you need 1/0.
You need to use a #6 copper, or #4 Aluminum for a ground.
If you run conduit, you can use #2 copper. If you use an NM-b cable (copper) you need 1/0.
IF you want to use aluminum cable you need 2/0. If its XHHW AL you need 1/0.
You need to use a #6 copper, or #4 Aluminum for a ground.
#4
09-03-14, 07:26 PM
Our main circuit box has 200A service, but not enough space for the 3 40A breakers (2 pole) that the system requires.
#6
09-04-14, 08:03 AM
I would advise you to have a load calculation done and also talk to your power company before attempting to add that much load.
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